Packages suitable for sterilization by heat treatment have been widely used in the field of flexible packages. Such packages are mainly used for packaging of retort foods, and they are popular because of their excellent convenience.
The contents of packages are usually removed by cutting a notched section of the package with the hand. However, when they have insufficient ease of cuttability or poor straight cuttability, the cutting path tends to veer toward the contents, or conversely the opening may be too small, making it impossible to remove the contents. In such cases, continued forced cutting by hand can cause the contents to spill or can result in the contents adhering to the hands or clothing. In cases of poor packaging cuttability, therefore, it has been necessary to using a tool such as a cutter or scissors to remove the contents, thereby resulting in reduced convenience.
Much research and development, such as described below, has been carried out in order to solve this problem.
Patent document 1 discloses a standing package wherein the contents are filled into a bag-like container comprising a barrel member and a bottom member formed of a laminated film, and the opening is heat sealed, wherein the barrel member is a laminated film comprising a biaxially stretched nylon film as the outermost layer, a uniaxially stretched polyolefin film or rolled polyolefin film as the interlayer and a film comprising a mixture of ethylene-vinyl acetate copolymer with linear low-density polyethylene as the seal layer.
Also, Patent document 2 discloses an easily openable independent package provided with a laminated package body comprising (a) a film composed mainly of L-LDPE, (b) a raw film composed mainly of Ny6, biaxially stretched to a factor of at least 2.8 in both the MD direction and the TD direction and (c) a biaxially stretched PET film, wherein the (a) film is a sealant layer, the (b) film is an interlayer and the (c) film is the outermost layer, and a tearing guide resin film, having a crystalline region with directional orientation, is laminated along the tearing section of the package body, a tearing notch being formed continuously across the tearing guide resin film and the package body.
Furthermore, Patent document 3 discloses a package for sealed packaging of moisture-containing foods, wherein a food package designed for high productivity as a food package, that can be utilized for heating or cooking while applying suitably safe internal pressure with a microwave oven or the like when the contents are to be used, is formed into a standing package form using a laminated film composed mainly of plastic, having a construction wherein, for example, the edge of one side is heat sealed with an air outlet path-forming seal solution so that an air outlet path with a bent structure that is sealed at the tip section is provided, and at the opening location at the tip section of the air outlet path there are provided a cutting line and a notch at its end, while at the top edge of the bag there are provided a cutting line on the opening for removal of the contents and a notch at its end.
However, even with these technologies it has not been possible to obtain high heat resistance and easy cuttability together with high seal strength and drop impact resistance.